CPU v. RAM Utilization

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T_Minus

Build. Break. Fix. Repeat
Feb 15, 2015
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How much more RAM are you adding
@realtomatoes

Sounds like you're playing it a bit close if adding a little more RAM is eating up ALL your CPU cycles on a DB server.... ???
 

realtomatoes

Active Member
Oct 3, 2016
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yeah, we keep a tight control on dishing out resources. most adds are generally 8GB and up depending on what code they added. these days my smallest db servers are 32GB VMs.
 

Evan

Well-Known Member
Jan 6, 2016
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Can be adding more memory just moves you along to the next bottleneck.
Nothing wrong with say oracle servers having 2 x 8-core cpu and 768gb ram, fast IO, the Target here is to make the cpu the bottleneck as that’s your licensing cost maximized.

I don’t know what @realtomatoes is actually saying though, sometimes the more of any resource can throw a nicely balanced system out and make it run in a loss optimal way, for example maybe a process was running slow was also allowing scheduling in of other processes but when it speeds up then it blocks everything else so the whole system suffers for a while (or user workload changes !)
 

realtomatoes

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Oct 3, 2016
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we generally push out large db servers towards physical boxes. we max virtual db servers at 16 vcpu and 96gb ram and tell them to scale out if they want to keep it virtual. that's why something like adding 8GB ram to a 4 vcpu 32GB VM can create a vcpu bottleneck and may need 2 more vcpu.

you are so right about the server workload really dictating it all. it's always a struggle to push our app people to scale out rather up.
 
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Patrick

Administrator
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Dec 21, 2010
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@Patrick, did you ever get a definite answer on this?
The answer is that all of our 128GB servers are going to be replaced by 256GB servers in the not too distant future.

We have too much CPU available and not enough RAM. Primarily because we have tons of CPUs and ebay gets us servers and SSDs (well last time we upgraded) at 15%-20% of retail. RAM is the bane of my budgeting.
 
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ullbeking

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Jul 28, 2017
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Concur, 'par for the course w/in Virtualization space' where memory to CPU consumption/allocation are in different worlds. We typically see approx 20% CPU usage by the time our memory is consumed @ 80% so a factor of 4 for us. HIGHLY dependent of course on CPU to memory balance/config and workloads.
@whitey are you saying that finding the right balance between CPU and memory in a physical box dedicated to one service or service type (eg, DB server) is going to be significantly different to finding the right balance on a virtualised DB server?

Although I definitely believe you, and I have experienced similar things too, everything I hear about this topic is based on anecdotes and hearsay. It would be so great if somebody has performed a proper, in-depth study, eg, like CACM article.